When the height (i.e. level) of a molten metal surface in a casting mold (mold) greatly fluctuates, impurities such as powder on the molten steel surface will be included into the steel that is in contact with the mold and being solidified. When the impurities are included into the steel, defects and/or cracks occur on the surface of the steel piece and are exposed in the form of a flaw or a scab on the steel plate at the time of rolling, having a significant influence on quality and yield. For this reason, it is required to suppress the fluctuations of the molten metal surface in the mold.
As an example of such a method of controlling the molten metal surface level in a mold, there has been disclosed in Patent Document 1, “a method of controlling a molten metal surface level in a mold of a continuous-casting machine”, for example.
The “method of controlling a molten metal surface level in a mold of a continuous-casting machine” disclosed in Patent Document 1 is “a method of controlling the molten metal surface level by measuring a molten metal surface level in a mold of a continuous-casting machine, inputting the difference between the measured value and a setting value into a feedback controller, operating an actuator based on the control output from the feedback controller, controlling, with the use of the driving power output from actuator, the amount of opening of a sliding nozzle that is provided for a tundish and used to supply molten steel, characterized by including: an estimation and calculation step of estimating periodic disturbance that causes molten metal surface level fluctuations based on the difference of the measured value of the molten metal surface level from the setting value and calculating the manipulated variable of adaptive control for cancelling the molten metal surface level fluctuations caused by the estimated periodic disturbance; and an operation step of operating the actuator, in which the calculated, manipulated variable of adaptive control is added to the control output from the feedback controller as a feed-forward value for changing the amount of opening of the sliding nozzle” (see claim 1 of Patent Document 1).